Interpretive Summary: Soil microbiology greatly impacts many important soil and plant processes and functions, including soil nutrient status, crop health, and overall crop productivity. One of the most important factors driving changes in soil microbiology is the particular plant species present. Yet, relatively little is known about the precise nature of these changes, how they occur, and what their effects are. A better understanding of the relationships among specific cropping systems, their resultant changes in soil microbial ecology, and their roles and effects on crop health and productivity is necessary for the development of more efficient, sustainable crop production systems. Potato production, in particular is in need of better crop rotations and sustainable solutions for crop and disease management problems. In this study, different 2- and 3-yr crop rotations with potato including barley/clover, canola, green bean, millet, soybean, sweet corn, and a potato control, were found to have distinct effects on soil microbia communities, as characterized by several different assay methods. These differences among communities associated with different crop rotations indicate the potential for rotation crops to be used to alter soil microbiology and improve crop health. With further studies, we hope to identify more specific changes associated with particular cropping systems and to relate these changes to effects on disease management, crop health, and crop productivity. This information is most useful to scientists, but with further elaboration of the effects of different crop rotations, extension agents and growers can use this information for the development of better rotations and more sustainable approaches to crop and disease management.

Technical Abstract:
The effects of different 2- and 3-yr crop rotations with potato on soil microbial communities were characterized over two field seasons by several parameters, including microbial populations determined by soil dilution plate counts on general and selective culture media, microbial activity measurements by fluorescein diacetate (FDA) hydrolysis, single carbon source substrate utilization profiles (from BIOLOG plates), and fatty acid methyl ester (FAME) profiles. Rotation crops evaluated in research plots at Newport, ME, included barley/clover, canola, green bean, millet, soybean, sweet corn, and a potato control. After one full rotation cycle (2 or 3 yrs), total populations of culturable bacteria, as well as overall microbial activity, tended to be highest in soil from rotations containing barley and canola, and lowest in soil from consecutive potato crops. Soil populations of fungi, however, were highest in soil from the consecutive potato plots. Principle component analyses of substrate utilization patterns demonstrated distinct qualitative and quantitative differences among rotation soils in their usage of carbon sources, including several carbohydrates, carboxylic acids, amides, and amino acids, in all fields in both years. Analyses of soil fatty acid profiles also demonstrated distinct differences among the rotations in their composition of fatty acids, indicating differences in their microbial communities. This research has demonstrated that different crop rotations have distinctive effects on soil microbial communities that are detectable using a variety of techniques. Further studies will identify more specific changes associated with particular rotations and relate these changes to potential effects on disease management, crop health, and crop productivity.